Blood Lead Level in Children with Neurological Disorders.

Objective
We aimed to investigate the blood lead level (BLL) in children with neurologic disorders of unknown causes and compare with normal children.


Materials & Methods
In this prospective case-control study, 68 patients aged 1 to 18 yr with neurologic disorders of unknown causes, were referred to pediatric neurology clinics and wards, Shiraz, Iran selected during a 12 months period from Sep 2013. They were compared with 1:1 ratio, age, and sex-matched healthy children. BLL was checked from all participants using 3 cc heparinized venous blood sample. Level of ≥5 mcg/dl was considered toxic dose.


Results
Totally, 136 children (68 cases and 68 controls) with mean ages of 5.20±4.12 and 4.18±3.86 yr, respectively, were enrolled. Mean BLL was higher in case group than in controls but the difference was not significant (P=0.84), though they were less than toxic levels in both. In addition, the difference in mean BLLs was not significant in terms of living place, sex, and age. Totally, 17.7% of the study sample had BLL ≥5 mcg/dl. The frequency of BLL ≥5 mcg/dl was significantly higher in case group (P=0.024) with an odds ratio 2.9 times higher (95% CI: 1.066-7.60).


Conclusion
Strategies in public health must focus on practicing primary and secondary preventions of lead exposure in children.


Introduction
"Lead toxicity has been one of the most significant preventable causes of neurologic morbidity from an environmental toxin" (1). While the immediate health effect of concern in children is typically neurological, it is important to remember that childhood lead poisoning can lead to health   (2,3). Patients may also suffer from brain edema, headache, and seizure.
Lead poisoning is most commonly seen in children from lower socioeconomic background.
As children absorb 50% of the lead they ingest, compared with the 10% absorbed in adults, children are more prone to lead poisoning (4).
Moreover, they are more likely to be exposed to lead from crawling around the floors and hand-tomouth activities (5). The growing child's brain has much greater sensitivity to lead than adult brain, and febrile convulsion, compared to that in normal counterparts (7)(8)(9).
The aim of this study was to determine serum lead level in children with different neurologic disorders and compare them with healthy ones.

Materials and Methods
In this prospective case-control study, patients with odds ratio is 2.9 times higher (95% CI: 1.066-7.60) ( Table 4).

Discussion
Although this study revealed no statistically significant difference in mean BLL between patient and control groups, they were below toxic levels (Table 3). However, the risk of having BLL ≥ 5 mcg/dL was 2.9 times more in patients with underlying neurologic disorders, compared to normal counterparts (P=0.024) ( Table 4).
The prevalence of lead toxicity has decreased in the United States since 1970s because of preschool screening programs, increased public awareness, and the removal of lead from gasoline and paint products (1, 6). In many parts of the developing countries, lead continues to be used in gasoline, pigments (e.g., in paint, cosmetics, and crayons), pottery glaze, solder, cooking vessels, and even medications. The normal hand to mouth activity of children causes them to be highly prone to lead toxicity. In addition, they absorb more lead from gastrointestinal mucosa than adults (4  nations and areas. In Iran, lead poisoning is more of a concern in urban areas due to the effect of industrialization. Likewise, the lead level is higher in Tehran, the capital city of Iran, compared with Shiraz, which is a less industrialized city (19).
In US during 1976 to 1980, children aged 24 to 48 months old with lead poisoning may not be identified due to lack of screening (20). Although preschool age was thought to be a risk factor for lead poisoning, children in this age group were also brought more to psychologists by their parents due to inattention problems and learning disabilities at school. Furthermore, the preschool children are more susceptible to toys related lead poisoning (20).
The present study demonstrated that the frequency of patients with BLL≥5 mcg/dl was significantly higher in groups with neurologic disorders than control one (P=0.024), consistent with some other studies (7)(8)(9). If on further inquiry these associations are found to be causal, lead exposure may represent a modifiable risk factor for this common condition of childhood. Lead poisoning is one of the most common and entirely preventable pediatric problems (1), strategies in public health must focus on practicing primary and secondary prevention of lead exposure in children.
The case group in this study included patients with seizure disorders, developmental delay and cerebral palsy, ADHD, encephalopathy and neuropathy. Patients with cerebral palsy, seizure disorders, ADHD and acute encephalopathy of unknown origin had higher levels of BLL (7)(8)(9).
In conclusion, This study was indicative of the toxic effects of lead on the nervous system. Although a level of 5 or higher is considered toxic, no level of vs.7.18 mcg/dl) the difference was not statistically significant though (13). The association of lower levels of lead (<5 mcg/dl) with the ADHD was also reported (14). A neuropsychology study in Cambridge comparing the preschool children being exposed to lead level <10 mcg/dl with their counterparts not being in contact with lead, the former group developed problems in doing their homework, maintaining attention and inability to restrain their automatic behaviors (15). A study examining children shortly after birth showed that apart from global intelligence, languagebased functions were often found to be affected.
Integrated postnatal rather than prenatal exposure is particularly deleterious, and no clear-cut effect threshold was found (16). However, in the present study, no statistically significant difference in BLL among case and control groups was detected.
However, mean BLL≥5 mcg/dl was more prevalent in the group with neurologic disorders (P=0.024).
As Shiraz is less industrialized with less air and water pollution, lower level of lead in children's blood was observed. Moreover, use of lead-based paints has been banned in Shiraz since 10 yr ago.
The current study did not show any significant difference in mean BLL between two groups in terms of age, sex and place of living. The reason could be insufficient sample size to evaluate the concurrent effect of these three variables. A study on 230 rural and 272 urban in south US demonstrated that rural children had lower BLL, compared with urban children (17). In contrast, in a study in North Carolina, the prevalence of lead poisoning was significantly higher in rural areas (18). These differences could be explained by varying amount and use of lead among different of China: a population-based study. PLoS One